The proposed research has been designed to use the microanalytical techniques of electron probe analysis to study the renal concentration process and to study the cellular response to anoxia. In the first part of the study mammalian kidney tissue will be prepared for analysis in the frozen-hydrated state in such a way so as to preserve diffusible element localization. Cellular elemental content will be determined in various parts of the nephron. Interstitial elemental gradients will be determined. Renal tubular luminal elemental concentrations will be determined all along the nephron. Solute concentration will be examined in various regions of the renal outer medulla to determine if there is functional compartmentalization corresponding to the well-known anatomical heterogeneity. Animals will be studied in various physiological states and after renal pelvic perfusion with various solutions previously shown to alter urinary concentration. With this phenomenologic information in various physiological states we will be able to evaluate theories of renal concentration mechanism and understand more adequately the method by which mammals can regulate salt and water excretion. In the second part of the proposed study the intracellular electrolyte composition will be determined in normal isolated cells grown in culture and in cells exposed to anoxia in the presence and absence of osmotically active agents in the media. Electrolyte composition will be determined by electron probe microanalysis. Cellular morphological responses to anoxia will be correlated with changes in electrolyte composition and ATP stores. The role of microtubules, microfilaments and calcium in the cellular response to anoxia will also be determined. By examining the pathophysiological response of isolated cells to anoxia as well as the determinants of cell survival in this state we will gain insight into the physiological mechanisms important to cell volume regulation. With this information it will be possible to identify interventions most likely to be effective in prolonging cell and tissue survival in animals and man under conditions of vascular insufficiency and ischemia.